The present invention relates to a method of making a digital photograph including the work of photographing a subject comprised of moving elements and still elements surrounding the same, in particular a subject including flowing water as a moving element, and improving the digital photograph by a computer image processing technique.
In the long practiced art of taking silver film photographs, when photographing a subject comprised of moving elements including water such as a waterfall or rapids and still elements such as the scenery surrounding them, as clear from the numerous photographs (clearly indicating the photographic conditions) described in for example Takao Otsuka, Utsukushiki Nihon no Kawa (Beautiful Rivers of Japan), taking the photograph at the so-called “slow shutter speed” of 1/30 second etc. has been recommended as a condition for photographing such moving elements. The specifications for the recently popularized digital cameras also follow this.
There is however still a doubt as to whether photographs taken by such a traditional photographic technique, leaving aside the aesthetic evaluation, can be said to substantially match with the actual visual perception. The present inventor has long held doubts over photography by this slow shutter speed in view of his experience in taking photographs during studies of the dynamics of high speed rotating objects.
It is known that, in the case of photographing a subject comprising a core formed by a moving water element such as a waterfall or mountain stream and still elements such as trees surrounding the core, if a high shutter speed corresponding to the running speed of the core is applied to take a photograph of such subject, the characteristic feature of the moving element can be captured as a photograph precisely, while the total image of the photograph becomes darker in comparison with the visual recognition by a normal human being. Therefore, the darkness of the photograph of the above-mentioned subject obtained by the high shutter speed cannot generally be accepted, in spite of the effective result indicating a realistic image of the moving element which is obtained by the application of the high shutter speed.
The applicant conceived that, if the above-mentioned problem due to the darkness of photograph can be eliminated under the condition of keeping the realistic image of the moving element, the photograph of the subject comprising the above-mentioned core and the still elements surrounding the core can be accepted in the photographic society. This is the origin of conceiving the present invention.
However, such changes in the darkness of a photograph are also affected by such conditions of the setting diaphragm of lens, and ISO sensitivity of the film used (note: in the case of using a Digital camera, setting value of ISO Sensitivity). Therefore, before arriving at the present invention, the following basic research for confirming the influence of the shutter speed on the darkness of the photograph was carried out in consideration of the influence of the “diaphragm condition”, “ISO sensitivity of film used (note: in the case of using a digital camera, setting value of ISO Sensitivity, by four successive experiments.
First Experiment
To achieve the object of the present invention, the present inventor studied what kind of shutter speed was suitable and whether photography by the so-called “slow shutter speed” which had been recommended in the case of photographing rapids, waterfalls, etc. was truly optimal for taking a photograph of a realistic image (first experiment). That is, he took photographs of the scene at the fountain plaza at the Imperial Palace Outer Garden (scene mainly of fountains) using a Nikon F-80 camera and ASA100 film (Kodak E100SW), setting the exposure compensation value to ±0 and the shutter speed divided into nine stages in the range of 1/15 second to 1/4000 second (details shown in Table 1), and using shutter priority AE. He then requested a local photo lab to develop the positive film, read the obtained film by a scanner of a second computer image processing system (owned by the present inventor), stored the digital data in a computer (Macintosh G3), and made a comparative study of the digital images displayed on the monitor. Further, the camera had the function of automatic adjustment of the diaphragm for maintaining suitable exposure. For reference, the diaphragm values corresponding to the shutter speeds are also shown in Table 1.
TABLE 1S: Shutter speed (seconds), V: Diaphragm, *SuitableExposure compensation value limited exceededFIG.SNo.(seconds)V11/15*22(+2)21/30*22(+2)31/6022(+1)4 1/125225 1/250166 1/500117 1/100088 1/20005.69 1/40002.8
TABLE 2EquipmentusedFirst systemSecond systemComputerMacintosh G4Macintosh G3MO driveOlympus Servo MOSame as first640CsystemScannerMicrotec ScanmasterSame as first4systemPrinterEpson 2000 CSame as firstsystemMonitorMitsubishi DiamondSame as firstRD 21Gsystem
Further, for convenience, when printing a digital image displayed on the monitor in the above-mentioned computer image processing system, if using a known color calibration technique, it is possible to easily make a digital photograph of color substantially matching the color condition characterized by brightness, contrast, chroma and color balance of the digital image, so in the following explanation, the “digital image displayed on the monitor corresponding to the digital photograph of FIG. X” is expressed as the “digital image of FIG. X” for simplification of the explanation. The above-mentioned color condition is hereinafter simply expressed as “color.”
As clear from FIG. 1 to FIG. 9, when the shutter speed is extremely slow ( 1/30 second or less), the contrast between the moving elements, that is, the fountains, and the still elements (the surrounding trees etc.) falls and the fountains are captured in just the state ofjets of water. As opposed to this, when the shutter speed becomes 1/60 second or more, the contrast between the moving elements and the still elements becomes higher and even the drops of water of the fountains are clearly captured, it is found. Further, it was learned that this change is related nonlinearly with the change of the shutter speed, that is, the change slows at a certain degree of speed or more (in this experiment, 1/500 second). Further, it was confirmed that the slower the shutter speed, the darker the photograph. When viewed visually, not just the state of the jets of water, but the state of the presence of falling drops of water in the jets of water is perceived in reality, so it was confirmed that taking a photograph at the above slow shutter speed is not in line with the object of the present invention. Note that it is self-evident that the same results are obtained even when using a camera not having the function of automatic adjustment of the photographic conditions, if adjusting the diaphragm value and the shutter speed by manual operation based on data clear from this experiment.
Second Experiment
Next, a commercially available digital camera (EOS D-30) was used to take photographs of the scene centered around the fountains in the Imperial Palace Outer Garden in the same way as the above-mentioned photographic experiment at an ISO sensitivity of 100 and shutter speed priority changing the shutter speed to several stages (shutter speeds etc. shown in Table 3). The digital data obtained by this was stored in the computer G4 of the first system shown in Table 2 from a CF card and the digital images (FIG. 10 to FIG. 23) displayed on the monitor.
TABLE 3S: Shutter speed (seconds), V: Diaphragm of lens, *SuitableExposure compensation value limit exceededFIG.SNo.(seconds)V101  *22 111/10*22 121/20*22 131/30*22 141/602215 1/1251916 1/2501617 1/3501318 1/5001119 1/750  9.520 1/1000 821 1/2000  4.522 1/3000  3.523 1/4000  *3.5
In this experiment (second experiment), photographs were taken at a constant of white balance condition exposure compensation value (±0) and a shutter speed set to a shutter speed of 14 stages from 1 second to 1/4000 second. The digital images obtained by this photographic experiment were studied compared with each other by FIG. 10 to FIG. 23. As a result, it was confirmed that the images almost completely matched the results of the above second experiment using a silver film camera. Therefore, a detailed explanation will be omitted. Further, since the camera had an automatic adjustment mechanism for automatically adjusting the diaphragm in accordance with a change in the shutter speed to maintain a suitable exposure, the diaphragm values corresponding to the shutter speeds are also given in Table 3 for reference.
Both when using a silver film camera and when using a digital camera by the above experiment, similar results are obtained, so in consideration of work efficiency, the above-mentioned digital camera was used in the following photographic experiments.
Third Experiment
Further, the third experiment was conducted with the intention of supplementing the above experimental findings.
That is, in this photographic experiment, the ISO sensitivity was fixed to 100, the shutter speed was set to 1/500 second, and the exposure compensation value was adjusted to the five stages of −2, −1, ±0, +1, and +2 to investigate the effects on the photograph quality. In the same way as the above experiments, photographs were taken giving priority to the shutter speed (AE). The changes in the diaphragm value were recorded, whereupon only naturally the diaphragm was set in such condition as 8, 5.6, 4.0, and 3.5. These photographic conditions are shown in Table 4.
TABLE 4S: Shutter speed (1/500 second), E: Exposure compensation valueV: Diaphragm, *Suitable exposure compensation valuelimit exceededFIG.No.EV24−28  25−15.626±04.027+13.5+2*3.5 
The results of the comparison of the digital images (monitor display) obtained in this experiment show, as shown in FIG. 24 to FIG. 27, that by moving the exposure compensation value to the minus side, the contrast becomes stronger at the details of the moving elements and the moving elements can be captured realistically as a result, but on the other hand the digital image gradually becomes darker.
Note that with an exposure compensation value of +2, the diaphragm of lens exceeds the minimum limit and the digital image also becomes too white, so this case was omitted from the series of attached drawings.
From the above experimental findings, it was confirmed that in order to photograph in particular a subject comprised of moving elements including flowing water and still elements and realistically capture even details of the moving water element, regardless of whether using a silver film camera or a digital camera, it is necessary to photograph it not by the so-called “slow shutter speed”, but by a faster shutter speed and it was confirmed that taking the photograph darker is desirable. Note that it was learned that the suitable shutter speed corresponds to the speed of change over time of the moving water element from the experimental findings of the later explained Embodiments 1 and 2.
According to the results of the above-mentioned experiments, it was confirmed that the dynamic feature of running water, such as a water fall or mountain stream, can be correctly represented as a photograph , if the photograph is taken at a shutter speed corresponding speed of the running water, although the entire photographic image becomes too dark so that the quality of the photograph cannot be accepted. Therefore, it is necessary to solve this problem.
In general, it is well known that the darkness of a photograph (digital image) can be easily corrected by applying a computer image processing technology which is disclosed in software such as Adobe Photoshop 5.5 (Registered Trade Mark), that is, such correction of darkness can be carried out by a simple modification of darkness, or the modification of darkness in relation to contrast, and accordingly by the modification of a tone curve. However, it is quite vague which type of corrections mentioned would be suitable to correct the darkness of the photograph created by applying a high shutter speed, and therefore, the following fourth experiment was carried out to clarify this problem.
Fourth Experiment
The fourth experiment was conducted to throw light on this question. That is, as the original digital image of this experiment and the comparative digital image to be used in the work, the digital images of FIG. 15 and FIG. 22 were selected from the digital images obtained in the above second experiment (for convenience, shown as FIG. 28 and FIG. 29). Further, the darkness of the digital image of FIG. 29, that is, the photograph taken at a shutter speed of 1/3000 second, was compared with that of digital images (FIG. 30 to FIG. 36) obtained by simply adjusting the brightness, adjusting a combination of the brightness and contrast, and adjusting the gradation, including adjusting the contrast for safety's sake, with the objective of correcting them to the brightness of the digital image (FIG. 28). As a result, it was confirmed that while the adjustment of just the brightness or the adjustment of just the contrast is completely unsuitable, adjustment by the latter two can be adopted. Table 5 shows the relationship between the content of the adjustment work and the drawings.
TABLE 5FIG.No.Content of image processing28Original image (same as FIG. 15)29Original image (same as FIG. 22)30Original image 29: Brightness adjustment (+35)31Original image 30: Contrast adjustment (+25)32Original image 32: Brightness adjustment (+30)33Original image 32: Contrast adjustment (+19)34Original image 33: Brightness adjustment (+50)35Original image 34: Contrast adjustment (+22)36OriginalThe brightness of the originalimage 29:digital image (input) and adjustedTone curvebrightness (output) are shown inTable 8 as input values and outputvalues for each of the tone curvesA, B, and C of FIG. 62.
Note that the fact that similar results are obtained by combined adjustment of the brightness and contrast and adjustment of the gradation can be understood from theoretical explanations relating to the parameters for physical evaluation of images, for example, Yoichi Mitake, Dejitaru Karaa Gazo no Kaiseki-Hyoka (Analysis and Evaluation of Digital Color Images) (page 91).
Here, when adopting the method of combined adjustment of the brightness and contrast for adjustment of the brightness of a digital image displayed on a monitor, the problem remains of what extent of adjustment of the brightness to perform first. It was confirmed that this problem is solved by the technique of adjusting the brightness of the original image (FIG. 29) to close to the brightness of FIG. 28 by adjusting the brightness, then adjusting the contrast to make the brightness of the digital image as a whole closely match that of FIG. 28. This fact is proved by the fact that when comparing FIG. 31 and FIG. 33, the brightness and contrast both substantially match.
Further, it was confirmed that it is possible to obtain similar results by adjusting the gradation by a known technique (adjustment of input and output of tone curve dialog box) (FIG. 36). For reference, the data of gradation adjustment is shown in Table 8 with reference to FIG. 62.
Note that FIG. 62 shows a known tone curve added with data display coordinates A, B, and C for the purpose of explaining the detailed content of gradation adjustment.
From this series of experiments, the photographic conditions for preparing a realistic digital photograph starting from a photograph obtained by photographing moving elements including flowing water and still elements and the technique for improving this digital photograph to a realistic digital photograph by computer image processing became clear. This is the crux of the present invention.